Alyeska (OTL Alaska) was discovered by Russian sailors coming from Novorossiya in 1583. After the Novorussian War of Independence, Novorossiya claimed all of Alyeska in 1644. The country was defended by a subdivision of the the Amur Army. 1652, Novorussians took Vancouver Island; and during the 17th century, Alyeska was expanded all the West Coast down to OTL San Francisco Bay.
1791, the first transoceanic telegraph cable (so to speak - it connected Alyeska with OTL Siberia) was built.
The difficult terrain of western Atlantis made it difficult to expand eastwards. While the other European nations settled lots of fertile lands, the Russians only could take influence on the Empty Circle. It was also difficult to get many settlers to their claimed lands. Thus, after the anti-French War the settlements of Britain, Italy and Germany reached the Rockies, meeting the Russians. Conflict was just a question of time, and came in 1848 with the anti-Russian War. The Russians lost and had to cede most of their lands in Atlantis in the peace of Constantinople to Canada (which gained access to the Pacific) and German Atlantis.